Brake adjusters

ABSTRACT

A slack adjuster for a vehicle braking system including first and second members having a normally reversible screw-thread connections therebetween, the first and second members are supported in first and second pistons respectively of the braking system and excessive displacement of the pistons causes relative displacement between said first and second member to reduce the displacement of the pistons on the succeeding stroke. One of the first and second members may be a split nut and a wedge member can be provided for urging the split nut against the other of the first and second members to prevent relative rotation therebetween under a brake-applying thrust.

United States Patent n91 Asquith 1 May 15, 1973 [54] BRAKE ADJUSTERS[75] Inventor: Anthony Asquith, Nuneaton, En-

gland [73] Assignee: Girling Limited, Birmingham, En-

gland [22] Filed: Mar. 30, 1971 [21] Appl. No.: 129,336

[30] Foreign Application Priority Data Apr. 3, 1970 Great Britain..l5,854/70 [52] U.S. Cl ..l88/71.9, 188/196 D [51] Int. Cl ..Fl6d 65/56[58] Field of Search ..l88/7l .9, 79.56 E,

188/196 B, 196 D, 196 BA [56] References Cited UNITED STATES PATENTS3,633,712 1/1972 Farr.... ..l88/196 D FOREIGN PATENTS OR APPLICATIONS1,319,419 1/1963 France ..188/7l.9

Primary Examiner-Duane A. Reger A ttorney- Scrivener, Park, Scrivener &Clarke 57 ABSTRACT 2 270 600 H1942 Ohlson ..188/I96 B first and Secondmembers to Prevent relative rotation 2:788:095 4 1957 Brooks ..l88/l96 Bthefebetween under a pp y thrust- 12 Claims, 1 Drawing Figure l l l I 40i PATENTED MY 1 51973 3 732 952 SHEET 2 BF 2 BRAKE ADJUSTERS The presentinvention relates to an automatic slack adjuster for vehicle brakes. I

i As is well known, it is desirable to limit the return travel of abrake actuating member, such as a hydraulic piston, of a vehicle brakesystem so that excessive pedal (or hand lever) travel will not beencountered the next time the brakes are applied. An automatic brakeadjuster may be provided which comes into operation as a result oftravel of such brake actuating member in the brake-applying direction inexcess of the desired travel. Upon such excessive travel the adjusteradjusts the limit of return travel of said brake actuating member whichoccurs when the brakes are released.

According to the present invention, a slack adjuster for a vehicle brakesystem includes two members having a normally reversible screw-threadconnection between one another and a further member is provided forurging the two first-mentioned members towards one another in a radialdirection with respect to the screw-thread connection and thereby intostrong frictional engagement with one another when a brakeapplying forceis applied between said two members.

Thus, the reversible screw-thread connection secures relative rotationbetween the two screw-threaded members when adjustment is required andthe further member acts to prevent the two screw-threaded members frombeing screwed back in the reverse direction when the adjuster issubjected to a brake-applying force.

A pawl and ratchet mechanism may be fitted at least indirectly betweenthe screw-threaded members to prevent unintentional reverse rotation inother circum stances.

Advantageously the adjuster is associated with a piston of a hydraulicactuator and an auxiliary mechanical actuator, such as a handbrake, actson the piston through the adjuster.

The invention is further described, by way of example, with reference tothe accompanying drawings, in which:

FIG. 1 is a sectional view of a hydraulic actuator of a reaction typecaliper disc brake of the kind described in British PatentSpecifications Nos. 1,075,371 and 1,147,639 and fitted with an automaticadjuster;

FIG. 2 is an exploded perspective view of the split nut of the adjusterof FIG. 1; and

FIGS. 3 and 4 are perspective views of two further embodiments of splitnut.

In the said reaction type caliper disc brake the hydraulic actuator isdisposed between a first disc pad and a yoke arranged for displacementrelative to the axis of the disc. The yoke extends to the side of thedisc remote from the first disc pad and supports a second friction discpad in opposition to said first disc pad. Expansion of the hydraulicactuator causes the first disc pad and the adjacent parts of the yoke tobe urged further apart so that the first and second disc pads arepressed against the disc. Contraction of the hydraulic actuator allowsthe first pad and the adjacent part of the yoke to approach one anotherso that the first and second disc pads can lose contact with the disc.

It will be appreciated that the actual displacement of the first padrelative to the second pad between braking engagement with the disc andthe disengaged positions of the discs is very small in this type ofbrake system and the direction of force applied by the hydraulicactuator is perpendicular to the plane of the brake disc.

Referring to the drawing, a hydraulic actuator comprises a pair ofopposed pistons 15 and 16 slidable in a through bore 17 in a fixed bodymember 18. The body member 18 is mounted at one side of a disc (notshown) and the piston 15 acts on a friction pad cooperating with thatside of the disc. The piston 16 acts on a yoke 19 which is slidablysupported on the body member 18 (as can be understood more fully fromthe above-mentioned Patent Specifications) and which acts on anindirectly operated friction pad at the other side of the disc.

An auxiliary mechanical actuator is also provided and comprises a cam 20which is jiournalled in an extension 21 on the piston 16 and which actsthrough a dolly 22 on a strut 23. The strut 23 forms part of anautomatic adjuster 24 which includes a split nut 25a, 25b, and a wedgemember 26. The adjuster 24 is for the most part accommodated within thepiston 15 which is hollow and the wedge member 26 is secured in the endof the blind bore 27 in this piston.

The nut 25a, 25b has a reversible screw-thread connection 28 with thestrut 23. A reversible screw-thread connection is a connection such thataxial displacement of the nut relative to the screw causes relativerotation therebetween and vice versa. Whether a screwthread connectionis reversible or not depends upon the pitch and flank angles of thethread and the coefficient of friction between the nut and the screw.The wedge member 26 has an internal frusto-conical surface 29cooperating with complementary surfaces 30 on the split nut 25a, 25b. Acompression spring 31 acts between the wedge member 26 and a ball race32 which engages a shoulder 44 inside the piston 15 and which cooperateswith a collar 33 on one end of the nut 25a, 25b to urge the split nut25a,. 25b to the left when adjustment is required.

A pawl 34 cooperates with ratchet teeth 35 on the wedge member 26 and isretained] on the nut 25a, 25b by a spring ring 36 and a Bellevillewasher 37.

Seals 38 seal the pistons 15 and 16 to the bore 17 and a seal 39 sealsthe strut 23 to a bore 40 in the indirectly operating piston 16. Alocating plate 41 held in place in the piston 16 by a spring ring 42prevents the strut 23 from turning relative to the piston 16 which isitself prevented from turning by the yoke 19. For this purpose thelocating plate 41 has a spigot 43 engaging in the piston 16 and has akey engaging in a keyway (not shown) in the strut 23.

During normal operation of the brake hydraulically, the hydraulic fluidis applied to the space between the pistons 15 and 16 to urge thesepistons apart and thereby urge the pads against the opposite sides ofthe disc. The hydraulic pressure acts on the left hand end of the strut23 to urge this strut to the right relative to the piston 15 and therebyholds this strut in abutment with the dolly 22, the cam 20 being held inits illustrated position by stop means (not shown). The clearancebetween the ball race 32 and the split nut 25a, 25b is sufiicient topermit relative axial movement between the two pistons 15 and 16 withoutaffecting the screwthread connection 28 during normal piston travel. 0nthe other hand, if there is excessive piston travel this clearance istaken up and the strut 23 tends to move the nut 25a, 25b further to theright against the force of the spring 31. However, rather than movefurther to the right the nut 25a, 25b is caused to turn on the strut 23by the reversible screw-thread connection 28 thereby effecting automaticadjustment so that the next time the pistons and 16 come to rest theycannot approach quite so closely towards one another.

When the handbrake is applied, the cam 20 is turned in an anti-clockwisedirection thereby urging the piston 15 to the left relative to thepiston 16 so that the brake pads are applied as before. However, in thiscase the brake-applying force is transmitted through the automaticadjuster, i.e. between the strut 23 and the split nut 25a, 25b. Sincethe screw-thread connection 28 is a reversible connection means must beprovided for preventing relative rotation upon handbrake application andthis means comprises the wedging surfaces 29 and 30. The brake-applyingforce is transmitted between the two halves 25a and 25b of the split nutand the wedge member 26 at these edging surfaces which thereby urge thetwo halves 25a and 25b towards one another thereby clamping the strut 23therebetween and preventing relative axial movement and consequentrelative rotation. The wedging surfaces 29 and 30 themselves act as afriction clutch further ensuring that the nut 25a, 25b cannot rotate.

The ratchet 34, serves to prevent the nut 25a, 25b from rotating in thereverse direction due to knock back and due to vibration.

While the split nut 25a, 25b is illustrated in FIGS. 1 and 2 as being intow parts it may be in a greater number of parts, e.g. three parts 45a,45b, 45c as shown in FIG. 3. Alternatively, the nut need not be splitinto several parts. Rather, as is shown in FIG. 4, the nut 46 may belongitudinally slit, at least in the region of the wedge member, and atthe same time have sufficient flexibility to enable it to be clampedagainst the strut. A further possibility is for the strut to be split orslit instead of the nut. In this case the wedge member extends insidethe split or slit strut and acts radially outwardly on the strut.

I claim:

1. A slack adjuster for a vehicle braking system including first andsecond members having a normally reversible screw thread connectiontherebetween such that in one direction of axial load between said firstand second members relative rotation is effected therebetween, and meanseffective upon axial loading in a direction opposite to said onedirection for urging relative radial displacement between said first andsecond members to hold the first and second members in frictionalengagement with one another at said reversible screw thread connectionto prevent relative rotation therebetween.

2. A slack adjuster as claimed in claim 1, in which said second membercomprises a longitudinally split 4. A slack adjuster as claimed in claim2, in which spring means is disposed between said second member and saidfurther member and acts therebetween in a direction to urge said wedgingsurfaces into engagement with one another.

5. A slack adjuster, for a vehicle braking system comprising first andsecond pistons disposed in a common cylinder and arranged to bedisplaced apart when a brake applying force is applied to the brakesystem, a first member slidably disposed within said first piston anddefining a screw-threaded portion extending at least partially into saidsecond piston, a second member within said second piston threadedlyengaged on said screw-threaded section and a further member engageablewith said second member for urging said second member radially intoengagement with said screwthreaded portion.

6. A slack adjuster, as claimed in claim 5 and wherein said first memberis restrained against radial displacement relative to the first pistonand is axially displaceable within fixed limits within said firstpiston, and said second member is rotatably disposed within the secondpiston and is slidably displaceable, within limits, within said secondpiston.

7. A slack adjuster as claimed in claim 5 and wherein a spring meansacts between the further member and said second member to urge saidsecond member radially into engagement with said screw-threaded portion.

8. A slack adjuster, as claimed in claim 5, and wherein excessive travelof the two pistons during a braking operation causes rotation of thesecond member relative to the screw-threaded portion of said firstmember whereby to reduce the travel of the pistons during a succeedingbraking operation.

9. A slack adjuster for a vehicle braking system including a cylinder,first and second pistons slidably disposed in said cylinder and adaptedto be displaced apart when a braking force is applied to the brakingsystem, a first member slidably disposed, in said first piston withinfixed limits and restrained against rotation relative to said firstpiston, said first member defining a screw-threaded shaft sectionextending into said second piston, a second member slidable androtatable within said second piston and defining threaded regionsengaged with said screw-threaded shaft, and a further member defined bya ring surrounding the said second member and presenting a conicalsurface for engagement with a complementary surface defined by saidsecond member, and means limiting the axial displacement of the secondmember within said second piston.

10. A slack adjuster as claimed in claim 9 and wherein the first part ofthe axial displacement of the second member relative to the secondpiston is unrestrained and further axial displacement, as the pistonseparation increases, is resiliently resisted by spring means.

11. A slack adjuster as claimed in claim 9 in which the second membercomprises a split nut presenting first and second end faces and definingnear said first end face a conical surface for engagement with saidconical surface of said further member and, at or near said second endface a radial flange, a thrust bearing, slidable on said split nutbetween said flange and said conical surface, and a compression springmeans between said thrust bearing and said further member.

12. A slack adjuster, for a vehicle braking system, including first andsecond members having a normally reversible screw-thread connectionbetween them, a further member surrounding said second member for urgingsaid second member radially towards said first member, and meansengaging said first member capafirst member and said cam and said cam,when rotated acting through the dolly to cause relative displacementbetween said first member and another moving part of ble of causing thebrakes to operate, said means includ- 5 the brake System Disclaimer3,732,952.-Ant7wny Asquith, Nuneaton, England. BRAKE ADJUSTERS. Patentdated May 15, 1973. Disclaimer filed Sept. 11, 1974:, by the assignee,Gz'rZz'ng Limited. Hereby enters this disclaimer to claims 4 and 7 ofsaid patent.

[Oyficz'al Gazette November 12, 1,974.]

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3732'952 Dated 1973 Inventor(s) Anthony Asquith It is certified thaterror appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

Claim 2, line 1 after "which" the following should be inserted:

-- said means for urging said radial displacement comprises a furthermember and Signed and Scaled this Ninth Day Of November 1976 [SEAL] Attes t:

RUTH C. MASON C. MARSHALL DANN Altesn'nx ()jficer (mnmissimu'r vjlalenlsand Trarlcmurkx

1. A slack adjuster for a vehicle braking system including first andsecond members having a normally reversible screw thread connectiontherebetween such that in one direction of axial load between said firstand second members relative rotation is effected therebetween, and meanseffective upon axial loading in a direction opposite to said onedirection for urging relative radial displacement between said first andsecond members to hold the first and second members in frictionalengagement with one another at said reversible screw thread connectionto prevent relative rotation therebetween.
 2. A slack adjuster asclaimed in claim 1, in which said second member comprises alongitudinally split member divided into circumferentially spacedportions having said reversible screw thread connection with andradially displaceable relative to said first member, and in which saidfurther member and said portions of said second member haveinterengageable wedging surfaces thereon for urging said portions ofsaid second member into frictional engagement with said first member. 3.A slack adjuster as claimed in claim 2, in which said second membercomprises a split nut, and in which said wedging surfaces compriseexternal and internal conical surfaces on said split nut and on saidfurther member, respectively.
 4. A slack adjuster as claimed in claim 2,in which spring means is disposed between said second member and saidfurther member and acts therebetween in a direction to urge said wedgingsurfaces into engagement with one another.
 5. A slack adjuster, for avehicle braking system comprising first and second pistons disposed in acommon cylinder and arranged to be displaced apart when a brake applyingforce is applied to the brake system, a first member slidably disposedwithin said first piston and defIning a screw-threaded portion extendingat least partially into said second piston, a second member within saidsecond piston threadedly engaged on said screw-threaded section and afurther member engageable with said second member for urging said secondmember radially into engagement with said screw-threaded portion.
 6. Aslack adjuster, as claimed in claim 5 and wherein said first member isrestrained against radial displacement relative to the first piston andis axially displaceable within fixed limits within said first piston,and said second member is rotatably disposed within the second pistonand is slidably displaceable, within limits, within said second piston.7. A slack adjuster as claimed in claim 5 and wherein a spring meansacts between the further member and said second member to urge saidsecond member radially into engagement with said screw-threaded portion.8. A slack adjuster, as claimed in claim 5, and wherein excessive travelof the two pistons during a braking operation causes rotation of thesecond member relative to the screw-threaded portion of said firstmember whereby to reduce the travel of the pistons during a succeedingbraking operation.
 9. A slack adjuster for a vehicle braking systemincluding a cylinder, first and second pistons slidably disposed in saidcylinder and adapted to be displaced apart when a braking force isapplied to the braking system, a first member slidably disposed, in saidfirst piston within fixed limits and restrained against rotationrelative to said first piston, said first member defining ascrew-threaded shaft section extending into said second piston, a secondmember slidable and rotatable within said second piston and definingthreaded regions engaged with said screw-threaded shaft, and a furthermember defined by a ring surrounding the said second member andpresenting a conical surface for engagement with a complementary surfacedefined by said second member, and means limiting the axial displacementof the second member within said second piston.
 10. A slack adjuster asclaimed in claim 9 and wherein the first part of the axial displacementof the second member relative to the second piston is unrestrained andfurther axial displacement, as the piston separation increases, isresiliently resisted by spring means.
 11. A slack adjuster as claimed inclaim 9 in which the second member comprises a split nut presentingfirst and second end faces and defining near said first end face aconical surface for engagement with said conical surface of said furthermember and, at or near said second end face a radial flange, a thrustbearing, slidable on said split nut between said flange and said conicalsurface, and a compression spring means between said thrust bearing andsaid further member.
 12. A slack adjuster, for a vehicle braking system,including first and second members having a normally reversiblescrew-thread connection between them, a further member surrounding saidsecond member for urging said second member radially towards said firstmember, and means engaging said first member capable of causing thebrakes to operate, said means including a dolly and a cam, said dollyextending between said first member and said cam and said cam, whenrotated acting through the dolly to cause relative displacement betweensaid first member and another moving part of the brake system.